The present disclosure relates generally to a method for forming a blown thermoplastic container, and more specifically in one embodiment to a "blow-and-blow" operation where a secondary opening is formed in a preform during the first blowing operation and then blow air is introduced through the secondary opening in the final blowing operation.
General blow molding techniques are well-established in the prior art, including both "single-blow" operations and "blow-and-blow" operations. An example of the "blow-and-blow" operation is disclosed in the U.S. Pat. No. 3,767,747, which is incorporated by reference.
One method of forming a blown plastic article according to the prior art includes inserting a blow pipe into one end of a parison which is enclosed within a blow mold cavity. Blow air under pressure is then introduced into the parison through the blow pipe to inflate the parison into the configuration of the desired article. This results in a blown article having an opening generally at the center of one of its axial ends.
When it has been desireable to form an opening in a blown plastic article at a position which corresponds to something other than an axial extremity of the article, it has been the general practice in the prior art to cut and trim the article in an operation subsequent to blow molding. This, obviously, presents the problems and disadvantages of additional and undesireable handling, equipment, time and expense.